1. Field of the Invention
The present invention relates generally to mine roof supports and, more particularly, to a set of mine roof supports designed to be nested.
2. Description of Related Art
Various roof support devices in the prior art have been designed and used to provide support to a mine roof. Deep mining results in removal of material from the interior of a mine, thereby leaving unsupported voids of various sizes within the mine. These unsupported voids are conducive to mine roof buckling and/or collapse. Thus, it has been desirable to provide support to mine roofs to prevent, delay, or control collapse thereof.
U.S. Pat. No. 5,308,196 to Frederick, herein incorporated by reference, discloses one commonly used prior art mine roof support. Specifically, the Frederick patent discloses a container that is placed between the mine roof and the mine floor and filled with a load-bearing material.
It is not economical to transport such containers for a mine roof support from the manufacturing site to the mine because of their overall size, which can be up to 15 feet in length and 72 inches in diameter, and weight. Because the containers are hollow, their weight is small relative to their volume. Therefore, the number of these containers which may be placed on a truck or railcar for transportation is limited by the volume of space that they occupy and not by their weight. Transportation costs are usually computed based on the distance that a load travels and not how efficiently it uses the available capacity of the transportation vehicle. Thus, the inefficient utilization of the available transportation capacity due to the combination of the high volume and low weight of the containers for the mine roof support results in high transportation costs relative to a load which more efficiently utilizes the capacity of the transportation vehicle.